The present invention relates to a process for the production of O,O-dialkyl pyrimidylphosphates.
Pyrimidylphosphates are known to be useful in the control of soil pests or insects such as corn rootworm, thrips, leafhoppers, and nematodes when applied to the soil of crops such as corn, sorghum, cotton, and sugar beets.
Processes for making these pesticides are also known. U.S. Pat. No. 4,094,873, for example, discloses a process in which an alkali metal phenoxide, pyridinoxide or pyrimidinoxide is reacted with an O,O-dialkyl-phosphoro-chloridothioate or O-alkyl phenylphosphonochloridothioate in the presence of a catalyst mixture under alkaline conditions in a liquid reaction medium. The catalyst mixture is made up of a quaternary ammonium salt and a diazole.
U.S. Pat. No. 4,147,866 also discloses a process in which an alkali metal phenoxide, pyridinoxide or pyrimidinoxide is reacted with an O,O-dialkyl phosphorochloridothioate in the presence of a catalyst mixture under alkaline conditions in a liquid reaction medium. The catalysts used in this process are a quaternary ammonium salt and a sterically unhindered, nucleophilic, tertiary amine. U.S. Pat. No. 4,147,866 also teaches that use of either the tertiary amine or the quaternary ammonium catalyst alone results in low yields, high amounts of unwanted by-products and expensive, difficult purification steps.
However, the use of two catalysts in the processes disclosed in U.S. Pat. No. 4,094,873 and 4,147,866 is disadvantageous because the cost of raw materials and product purification is increased.
U.S. Pat. No. 4,429,125 discloses a process for the production of phosphorus esters of 5-pyrimidinols in which a 5-pyrimidinol is reacted with a phosphorochloridothioate in an inert organic liquid in the presence of an acid binding agent or acceptor. The acid binding agent or acceptor is selected from alkali carbonates, alkali hydroxides and alcoholates such as sodium carbonate, potassium carbonate, sodium or potassium methoxide, sodium or potassium ethoxide, and amines. No phase transfer catalyst is included in the reaction mixture.
U.S. Pat. No. 4,729,987 also discloses a process in which a 5-pyrimidinol represented by a given formula is reacted with a phosphorochloridothioate in an inert organic liquid and an acid binding agent or acceptor at a temperature of from about 0.degree. to about 100.degree. C. No phase transfer catalyst is included in the reaction mixture.
Published European Patent Application 277,292 discloses a process for producing O-pyrimidinyl phosphorus compounds in which an aqueous solution of a salt of a pyrimidine is reacted with a phosphorus ester in the presence of a phase transfer catalyst without added organic solvent. This disclosure teaches that low yields are to be expected when an organic solvent such as toluene is used as the reaction medium.